Attached Link: http://www.morphography.uk.vu/bumpmaps.html

Changing the skin texture to greyscale rarely makes a good bumpmap by itself. You'd be better making your own. Start with a 50% grey fill; then colour "sticking out" bits lighter, and "sticking in" bits darker. If making the scars protrude is your aim, that's all you need to do. Making a full skin bumpmap is a more complex art, and I'll leave that to the people who actually know how to do it. :) What version of Poser will it be for? Be aware that Poser 4 for Windows converts bumpmaps wrongly, but you can correct them afterwards. (See link)